Electroplating and electroetching are manufacturing techniques used in the fabrication of metal and metal alloy films. Both of these techniques involve the passage of current through an electrolytic solution between two electrodes, one of which is the target to be plated or etched. The current causes an electrochemical reaction on the surface of the target electrode. This reaction results in deposition on or etching of the surface layer of the electrode. In the plating or etching of thin metal films disposed on a non-conductive substrate, the current tends not to be uniformly distributed over the surface of the target. This non-uniformity is attributed, at least in part, to the so called "terminal effect", i.e., the influence on plating distributions of ohmic potential drop within the thin metal film that acts as an electrode. This effect is exacerbated with increased wafer sizes, decreased seed layer (metallized film) thickness and decreased final deposited layer thickness (often less that 1 um (micron) in newer designs.
Control of the uniformity of the deposited or etched layer on the target electrode surface (sometimes referred to as the substrate) is particularly important in the fabrication of micro-electronic components. Uniformity is an important consideration when electroplating or electroetching is used to make thin-film electronic components, including resistors, capacitors, conductors, and magnetic devices such as propagation and switch elements. U.S. Pat. No. 3,652,442 issued to Powers et al. and U.S. Pat. No. 4,304,641 issued to Grandia et al. disclose electrolytic processes and apparatus in which alloy and dimensional uniformity are important factors.
In a cup plater, which is often used in the manufacture of small thin-film electronic components, plating uniformity is controlled, to some extent, by system geometry, bath composition, bath flow control, and operating conditions. In one such cup plater (known as "EQUINOX", available from Semitool, Inc.) a baffle, disposed between the target electrode and the counter electrode to affect ion distribution, comprises a plate with a plurality of uniform, and uniformly distributed holes. Nevertheless, a condition known as "edge effect" remains a problem. Edge effect manifests itself as the non-uniform thickness that occurs on the edges of a target electrode surface as it is etched or plated.
An object of the present invention is to provide improved electroetching and electroplating apparatus and methods to achieve relatively uniform distribution over the entire surface of an electroetched or electroplated thin metal film, and particularly at the outer edge of the metal film.